Unfolded proteins and their interactions are assuming increasing importance in studies of cellular metabolism, as functional unfolded forms of many regulatory proteins are discovered. Many disease states are linked to unfolded and misfolded proteins. Molecular chaperones frequently contain unstructured or partly structured domains whose functions are poorly understood. The first three specific aims of this project address a postulated function of these unfolded domains in binding of peptides and unfolded proteins. A novel observation from preliminary data is that in two cases these domains appear to form molten globule-type structures in solution. The first domain to be studied (Aim 1) contains the cysteine-rich (CR) and C-terminal domains of Escherichia coli DnaJ, which appears to form a molten globule. A molten globule also appears to be formed by the C-terminal domain of the E. coli chaperone trigger factor (Aim 2). In each of these cases, the structure of the molten globule state will be probed by NMR methods, and insights into the function will be provided by binding of peptides and unfolded proteins. The third domain (Aim 3) is p23, a human Hsp9O co-chaperone, whose unfolded C-terminal sequence is required for chaperone function. Constructs containing the folded N-terminal domain and the unfolded C-terminal sequence will be studied by NMR to determine the sites of binding of Hsp9O and unfolded proteins. The fourth Aim is concerned with a solution structural study of a quorum-sensing factor, SdiA, which has been implicated in virulence of pathogenic E. coil strains. A requirement for a small molecule autoinducer has been found before another quorum-sensing protein, TraR from Agrobacterium tumefaciens, can fold in the cellular environment. The structure and folding behavior of SdiA will be determined, in order to discover whether this behavior is general in bacterial quorum-sensing. These four specific aims are directed towards the overall goal of this research project, to elucidate the relationship of structure and function in protein systems with one or more unfolded components, in order to further our understanding of the role of folding and unfolding reactions in cellular metabolism and disease.